Large triangular polygon with a large number of points in the mesh - unity3d

Question

When creating the mesh, I had a problem: both in the game, and in the scene appears a large triangular polygon. The problem is that with a system size of 250 by 250 points there aren't this polygon. At a size of 400 by 400 points, it already appears.
What I did:
void Start () {
MeshFilter mf = GetComponent<MeshFilter>();
Mesh mesh = mf.mesh;
int size = 400;
Vector3[] vertices = new Vector3[size * size];
Vector3[] normals = new Vector3[size * size];
Vector2[] uvc = new Vector2[size * size];
int c = 0;
for (int i =0; i < size; i++)
{
for(int j =0; j < size; j++)
{
vertices[c] = new Vector3(i, j, Mathf.Sin(j+i+Mathf.PI));
normals[c] = -Vector3.forward;
float mult = 1.0f / ((float)(size));
uvc[c] = new Vector2(((float)(i))*mult, ((float)(j)) * mult);
c++;
}
};
int[] triangles = new int[(size-1)*(size-1)*6];
int counter = 0;
{
for (int i = 0; i < size - 1; i++)
{
for (int j = 0; j < size - 1; j++)
{
setTriangle(ref triangles, ref counter, i * size + j);
setTriangle(ref triangles, ref counter, (i + 1) * size + j);
setTriangle(ref triangles, ref counter, i * size + j + 1);
setTriangle(ref triangles, ref counter, (i + 1) * size + j);
setTriangle(ref triangles, ref counter, (i + 1) * size + j + 1);
setTriangle(ref triangles, ref counter, i * size + j + 1);
};
}
};
mesh.Clear();
mesh.vertices = vertices;
mesh.triangles = triangles;
mesh.normals = normals;
mesh.uv = uvc;
mesh.RecalculateNormals();
gameObject.transform.position = new Vector3(-55, -60, 90);
void setTriangle(ref int[] triangle, ref int index, int num)
{
triangle[index++] = num;
}
And what I have in results. The first picture is with 250 by 250 points. The second is with 400 by 400. The third is just bigger picture

Answer 1

I think you are over the max. number of vertices for the mesh when the size is 400x400.
The default max. number of vertices for a mesh is 65535. If you want to have more, then you have to set:
mesh.indexFormat = Rendering.IndexFormat.UInt32;
but this is not guaranteed to be supported in all platforms.